The Transient Impact of Ozone Depletion on the Southern Hemisphere Ocean: Sea Surface Temperature, Heat Content, and Carbon

There is strong evidence that Antarctic ozone depletion has significant impacts on surface weather patterns, including driving a positive trend in the Southern Annular Mode (SAM). Here we discuss recent advances towards understanding the impact of these changes on the Southern Hemisphere ocean. With a focus on the time-dependence of the ocean response, we perform experiments using six coupled climate models in which ozone concentrations are abruptly perturbed from preindustrial to modern conditions.

In the Southern Ocean (poleward of 50ºS), the response of sea surface temperature (SST) to ozone depletion involves two time scales, consisting of a rapid cooling of SST, followed by a slower warming trend. Although this basic response is robust, comparison across models reveals large uncertainties as to its time scales and amplitudes. In midlatitudes (between about 30-50ºS) the SST response consists of a simpler, warming trend in all models. Midlatitude surface temperature anomalies are transported to depth by increased ventilation and subduction, leading to a redistribution as well as a net increase ocean heat content. Significant changes are also demonstrated in both the directly-forced and biological storage of carbon in the ocean. However, we show that these two effects may approximately cancel, leading to a small net impact on ocean carbon, the sign of which is uncertain. Finally, we discuss the relationship between our idealized experiments and responses to realistic time-varying ozone concentrations, as well as implications for attributing the role of ozone depletion in observed ocean trends.